Dilemma, been bothering me for a while

" I get that someone shouldn't ask someone out until they're good with the friends"

Exactly. And you already know one of her friends. Her best friend. Who is your ex.

She's your Ex's best friend, so its never ever ever ever going to work. I promise you that. It will never work. And your ex, even if tomorrow she turned into your best friend in the world and for the rest of your life was nothing but a friend: she will make sure it does not work between you and this girl. Promise.

You don't know that for sure - it is your presumption.

How long were you dating your ex-girlfriend? How serious was it?

That makes a big difference I think.

Also, how big is your school?

My perception may be skewed because my (10th-grade) daughter goes to a small school, but for her, if there were an absolute avoidance of dating friends of previous GFs/BFs, nobody would have anyone left to date by now. There are many, many couples I can think of where one of them dated one of the other person's close friends in the past -- best friend, even.

However, I don't think any of those previous relationships were really serious.

What makes you think this new girl is interested in you? You don't mention if she is giving you signals that she wants anything more than just friendship.

I'll try to answer all your questions at once. We dated for about a month before she dumped me, she left me so she could sleep with one of my sisters friends(just to get this out of the way, my sister hasn't slept with him) only to move onto his romate, then to like 5 new boyfriends, before she stopped on her current one. The first guy she left me for is now dating/having sex with another girl in my ex/crush's circle. The other, and final one in our circle is dating one of my friends, although we aren't very close. The one that is sleeping with/dating my sisters friend doesn't like me at all(I don't get what I did to her, she never liked me until I went to homecoming with her friend/my ex, afterward she went back to hating me). The one dating my friend and I get along fine, although we don't talk very much. My ex and I have very restricted and taught conversations, usually very Ahkward and short.
Between my crush and i, we talk sometimes, usually joking around.
As far as signs, that was my first girlfriend ever, and I really don't know if she'd be sending me signals, if she is they're going over my head.
The school has about 900-1000 student population, though, since we're all in band, it's a much lower number of people I'd be worried about. There are about 140 people in the band, 30-50 colorguard adding to that.
I am on the drumline, crush is in the trunpet section, my ex and the other two are in the colorguard.
We dated for about a month, and in those few weeks, it never got serious, like I said, we never had sex, we never kissed except for on the cheek at homecoming, and that's about it.
If I didn't answer one of your questions, just reply so to this and I will. Thanks.

Based on what you wrote, you only went out a few times over a month but she wasn't your g/f. You're free to date whoever you want. Why make this difficult.?

I am neither agreeing or disagreeing with you, but taking it under consideration. Her friend(the one that is dating my friend) before homecoming pulled me to the side at a competition and told me she considered us dating. In their, if not her mind, we dated. Would you consider this a problem? You have to remember though, this is the friend that i get along with.

Stop getting your information and signals from OTHER people.

This is between you and this girl. Get up the courage to develop a relationship with her - and the heck with everyone else.

You DO pay too much attention to the lives of other people, you know.

Yeah, I don't see any red flags there for you dating your crush. Seems like the previous relationship was brief and not particularly meaningful.

Go for it, same as you would with anyone else you'd have a crush on.

That of course doesn't mean that your crush will reciprocate. Just, there doesn't seem to be enough to this previous relationship for you to have any reason to avoid even approaching her.